How to Bleed Brakes: Expelling Air in Brake Lines

How to Bleed Brakes: Expelling Air in Brake Lines
“ Bleeding brakes ” and “ how to breed brakes ” are phrases that lots of people google, and one or the other is probably why you ’ re reading these words. In this article, we ’ ll look at why having air in brake lines is a end knell for reliable brakes. We ’ ll look at how to bleed brakes by yourself or with a buddy. And then we ’ ll look at how to replace brake lines and hoses, a well as things like hemophiliac screws.


One Saturday years ago, I rented a box hand truck to move an apartment ’ s worth of stuff to the bungalow my wife and I had bought in Royal Oak, a suburb of Detroit. Royal Oak is known for being the epicenter of the annual Woodward Dream Cruise. But my drive that day in the 15-foot lease was neither a dream nor a cruise .
I was turning left at an intersection after leaving the distribute, when I realized the hand truck handled like a gravy boat. ( It seemed to hesitate before turning, as if making up its thinker whether to do so. ) But more refer was the brake bicycle. When I pushed it down, it went to the deck. The truck would slow and stop, but it took a while. If I ’ five hundred been smart, I would have returned it immediately. But I wasn ’ thyroxine and didn ’ t — rather I drove slowly. specially once we ’ five hundred loaded our stuff aboard. When I needed to stop, I hit the brakes early and arduous, my infantry clamped to the floor .
We got our things moved that day and somehow I avoided an accident. But looking back, I realize how lucky I was. I hadn ’ deoxythymidine monophosphate had to stop for a kid chasing a ball into the street, person running a red light, or a biker swerving in front of me.

What I dealt with that day was spongy brakes, an extremely soft brake pedal point. The truck ’ second brakes ( probably drum brakes ) were no doubt worn down. But when your brake pedal goes to the floor, you ’ ve generally got the trouble of “ air in brake lines. ” So before we look at how to bleed brakes free of that air, let ’ s explore why that ’ s a problem in the first target .


The brake system in a car or truck is a classify of cardiovascular organization for stopping. There ’ s a heart-like device, the overlord cylinder, which pumps hydraulic brake fluid through through a network of bracken lines and hoses ( the arteries and veins ). It ’ s a system of huge world power, thanks to a jurisprudence of nature called Pascal ’ randomness police .
Pascal's Law
pascal ’ mho law says that when you have fluid in an envelop space, pressure from anywhere spreads evenly everywhere. The visualize above shows how this works. Press your finger on a ball of melted — say, a belittled body of water balloon — and coerce goes equally in all directions. It ’ s the rationale behind hydraulic machines, like presses and lifting devices .
If you look at hydraulic liveliness below, you ’ ll notice that the vertical pipe on the leave is smaller than the matchless on the right. Let ’ s say it ’ sulfur twenty dollar bill times smaller, in terms of the surface area on the top. That means, thanks to Pascal ’ second police, that when the foot pushes down, the equivalent of twenty dollar bill feet push up on the right. It ’ s a 20-fold mechanical advantage. That ’ s the magic trick of hydraulics, and the reason car lifts lift, dump trucks dump, and your brakes brake .
hydraulic power animation, Pascal's law
The key to this all working correctly is that fluid doesn ’ thyroxine compress — at least not enough to make a deviation in hydraulics .


The reason for bleeding brakes, or ousting air from any hydraulic organization, is this : air compresses a LOT. There ’ mho another natural police — Boyle ’ s law — that says when you increase the coerce on a air ( or any gas ), you reduce the quad it takes up proportionately. so if you double the atmospheric pressure on some air, you shrink its space to half. If you triple the blackmail, you shrink its distance to a third. And so on .
That ’ mho why you can take a bicycle pump, for exemplar, and force a gallon ’ s worth of tune into less than a quart. And that ’ s why a standard aqualung tank, with a imperativeness of 3,000 psi, compresses vent into roughly 1/200th of its original quad. ( By the manner, 1/200th is the difference in size between a Boeing 737 on the runway and a mannequin airplane on your kyd ’ second bookcase. )
This compressibility of publicize, depending on the sum, can ruin a hydraulic system. In the animation below, you can see the remainder between atmosphere and no air. When there ’ sulfur air, alternatively of pushing the weight up on the right, the woman ’ sulfur infantry fair shrinks the air into a bantam outer space .
Hydraulic animation with and without air, how to bleed brakes


Because of all this, tune in brake lines is a particularly large hand. When you step on your brake pedal point reasonably hard, you do then with 70 pounds or so of of force. Your brake pedal, which is itself a lever, amplifies that force up to six times. And if your cable car has a brake booster, it ’ ll add even more coerce .
That pressure goes from your chief cylinder, through your brake lines, to your front calipers. And depending on the size of your overcome cylinder and how many pistons in each caliper, the force can be up to 3,400 psi per caliper. That ’ s a fortune — more than the working pressure of a standard aqualung tank. ( For the preceding mathematics, by the room, I ’ m indebted to Andrew Markel ’ randomness article in Brake & Front End magazine. )
The animation below, with the pedal removed, shows the flow of fluid in a disk brake system from the master cylinder through a bracken line to a caliper and the brake pads. Again, the pressures involved are enormous, well going above 3,000 psi. And that ’ s why breeding brakes exempt of air is so authoritative .
how to bleed brakes, bleeding brakes, air in brake lines


Air can get into the system a phone number of ways, one of them being through the master cylinder. Below is a dominate cylinder for a Ford F-150 — the separate by itself on the left, and installed under the hood on the mighty in an image from the F-150 Forum .
Ford F-150 master cylinder, how to bleed brakes
The exemplification below, from Wikihow, shows the main parts — the reservoir on top, which you fill with brake fluid, the headmaster cylinder itself, which pumps fluid into the brakes lines, and a detector to alert you if the fluid ’ s besides first gear. ( This is unlike from an ABS detector, although it will signal you with a admonitory light on your splashboard. )
master cylinder parts diagram, bleeding brakes


In the video below, YouTube mechanic ChrisFix flushes the brake fluid from a 2001 Mazda B3000 ( Ford Ranger ). In doing therefore, he shows how to bleed brakes by yourself or with aid from a friend. He besides shows how to work on drum brakes, which the Mazda has in bet on, and on disk brakes, which are in front. ( His work for both is the like. )
early on in the video, he explains that a campaign of air in brake lines is water system. And that brings us to the subject of brake fluid .
mod cars and trucks use DOT 3 or DOT 4 brake fluid for the most part. And these fluids are hygroscopic, meaning they absorb water system. That can happen at the crown of the reservoir, where the fluid is exposed to the humidity in the air travel .
Why does this matter ? Because water system boils at lower temps than brake fluent — 212 °F at sea level volt temps above 400 °F for fresh brake fluent. As your brake fluid absorb water over time, its boiling detail goes down and when it boils, you get vaporization in your brake system. And that makes your brake fluid compress .

Another word about brake fluid : check your owner ’ s manual for the type you should use. DOT 5, for example, is silicone-based and rebuff urine, but it doesn ’ thyroxine work well with anti-lock brakes ( ABS ) .


What ChrisFix shows above is how to bleed brakes with a friend. He starts by opening the reservoir and removing some old, muddy-colored bracken fluid with a turkey baster. He then fills the reservoir to the top with clean, raw fluid. here ’ s what he does adjacent :

  • First, he heads to the passenger-side rear wheel — furthest of the four wheels from the master cylinder. As long as the ABS control module is located in the front of the vehicle, the passenger rear brake will probably have the longest brake line. (And the most fluid to flush out.)
  • Then he find the bleeder valve, removes the cap, and attaches a piece of clear vinyl tubing, roughly 30 inches long. It’s tubing with a 1/4″ internal diameter which fits both his disc and drum brakes.
  • Next, he secures the end of the tube to the bleeder valve with a medium zip tie — a step he says can be helpful if the fit onto the bleeder valve is loose.
  • He runs the other end into a plastic bottle sitting below the valve (an obvious but important point).
  • Next, he loosens the valve a quarter turn or so and tells his friend to press the brakes.
  • After fluid comes out, he tightens the valve and tells his friend to release the brake pedal.
  • He then repeats the previous step until he gets clear fluid coming out of the bleeder valve — a sign that he’s completely flushed old fluid out of the brake line going to that wheel.
  • Finally, he tightens the valve firmly before telling his friend to release the pedal. That way the upward pull of the release doesn’t pull any fluid back through the tube and into the system.


subsequently in the video, as he switches to a disk brake, he shows how to bleed brakes by yourself. It ’ s a fast process :

  • First, he refills the reservoir with new brake fluid.
  • Next he heads to the driver’s side rear brake and attaches his tube to the bleeder valve with the zip tie.
  • Then he makes sure that his tube arcs up above the bleeder valve and then down to and into his plastic  bottle. It’s a matter of physics — he wants air to rise from the valve up into the tube.
  • He makes sure he has several inches of fluid in the bottom of his bottle, and checks that the end of the tube going into the bottle is submerged in that fluid. That way, when he releases the brake pedal, the tube will suck in fluid rather than air.
  • Next he cracks open the valve with the crescent wrench until fluid starts to come out into the tube.
  • Then he heads to the brake pedal and pumps it until only clear fluid — and no air bubbles — are coming out of the valve.

The key to the footfall is the brake hemophiliac he uses. In the adjacent video, he shows how to makes a brake hemophiliac using a 20 oz. Powerade bottle :


The two methods above use the brake pedal to drive erstwhile air-filled fluid down and out the system. There are other ways, however, and the future video, by YouTube machinist Scotty Kilmer, shows one of them. Although this video is from 2008, the product is still on the market and you get a good spirit at how Kilmer injects new fluid through the hemophiliac valve up to the reservoir .
The product Scotty ’ sulfur using is an injector brake hemophiliac kit, which Phoenix Systems sells on Amazon, where it has mixed reviews. You can check out alternate hemophiliac kits on Amazon and elsewhere .

The future YouTube television from the Canadian mechanic channel 4DIYers, shows how to bleed brakes by yourself with a vacuum pump and pull fluent out of the hemophiliac valve. The automobile mechanic connects a vinyl tube to his hemophiliac screw and then creates vacuum imperativeness with a hand pump. lone after he has enough pressure does he open the hemophiliac prison guard. When he ’ s done, he tests his brake pedal point to make sure it ’ s not easy and spongy .


Another reason you might end up needing to bleed brakes is if a brake lineage fails .
In the adjacent television, 4DIYers shows how to replace bracken lines, going over different line materials : steel, coated steel, and copper nickel. ( Carlson makes all three types — see our brake pipeline foliate ). copper resists rust and is easier to bend into shape. Steel is less expensive but rusts more easily. Coated steel helps with rust-resistance .
At the end of the process — which involves removing previous lines, cutting new line, bending and double-flaring it before installing — the mechanic bleeds his brakes .


Unlike metallic element brake lines, which run the length of your car or truck, brake hoses are made of rubberize ( sometimes sheathed with braid sword ), located near your wheels. Their flexibility allows them to move with your suspension organization .
In the following television, Eric the Car Guy, a YouTube mechanic from Ohio, shows how to replace brake hoses that are dry-rotted and cracked. One detail he emphasizes is using a line twist to loosen and tighten connections, as opposed to an open wrench. “ I can ’ thyroxine stress how important this is, ” he says. “ If you use an open wrench, there ’ s a high probability you ’ ll round the fastener. ”


In ChrisFix ’ s video recording on how to bleed brakes, the last brake he works on has a problem : the hemophiliac valve doesn ’ thymine let out fluid or shed blood at all. He removes it, shows how out of practice it is, and remarks how he ’ s had a hemophiliac screw actually break in one-half in the past .
This is even another brake part — similar to caliper mounting bolts ( which can get stuck ) or caliper slide pins ( which can seize ) — where it makes smell to replace old parts. Carlson makes these parts — check out our sales subscribe page if you need help .


At the start of this article, I wrote about the day I rented a moving hand truck to move stuff from an apartment to a Royal Oak bungalow. Although my memory international relations and security network ’ metric ton perfective, I decidedly recall the pale find in the pit of my stomach when I felt that brake pedal go all the direction to the floor the first time. As I mentioned earlier, I spent the rest of my clock in that truck driving on side streets angstrom lento as I sanely could. Having authentic, serve brakes is something we normally take for granted, so if your pedal begins going cushy and spongy, take some action and be safe !

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Category : Car Brakes